refactor(search): adopt the Microsoft Web IQ contract

[Menci]

Agent: Codex, an AI coding agent.

Summary

• adopt Microsoft Web IQ across the provider discriminator, implementation module, control-plane types, dashboard copy, errors, telemetry, and tests
• migrate persisted search configuration credentials and usage buckets to the Web IQ schema without losing existing records
• advance data-transfer payloads to version 18 so exports and imports use the same Web IQ configuration and usage contract

The Microsoft Web IQ portal documents api.microsoft.ai/v3 as its REST API base: https://webiq.microsoft.ai/documentation/quick-start/

Test Plan

• Run pnpm run lint
• Run pnpm run typecheck
• Run pnpm run test — 422 files and 4,905 tests passed
• Apply migrations through 0068 to a fresh SQLite database, seed the previous configuration and usage shape, then apply 0069_microsoft_web_iq.sql
• Verify the migrated credential, Web IQ usage totals, unrelated Tavily/Jina rows, removed legacy column, removed legacy provider rows, and PRAGMA foreign_key_check